The present invention relates to electronic portable appliances to be driven on generation power of a power generating means or the like and, more particularly, to an electronic portable appliance provided with a power feed means having a power generating means or a generating means and booster circuit to increase the voltage of the power generating means, a power storing means to store power supplied by the power feed means, and a drive circuit driven on power supplied by the power feed means or on storage power of the power storing means, for use in a wrist watch driven on power supplied from a thermoelectric conversion device, solar battery or the like.
There is shown in FIG. 6 a schematic block diagram of an electronic portable appliance according to a related art. In FIG. 6, an electronic portable appliance 600 is configured by a power feed means 10 for supplying electric power, a power storing means 40 for storing power supplied by the power feed means 10 through a diode element 601, and a drive circuit 50 to be driven on power supplied by the power feed means 10 through the same diode 601 or on storage power built up on the power storing means 40. Furthermore, the power feed means 10 is formed by a power generating means, a booster circuit for increasing the voltage of the power generating means and so on.
In such an electronic portable appliance, the power feed means 10 is also required to be reduced in size and weight due to the reductions of size and weight of the appliance. Due to this, there is a tendency toward decreasing the power supplied by the power feed means 10. On the other hand, there is a desire to improve the charge efficiency to the power storing means 40 and effectively utilize the power stored on the storage means 50, due to a desire for increasing the operating time of the electronic portable appliance.
Accordingly, to realize the further reduction in size and weight or further increase in operation time for the electronic portable appliance, it is indispensable to further increase the charge efficiency to the power storing means and effectively utilize the storage power on the power storing means.
In the related art electronic portable appliance, rectification is made by the diode element 601 in order to prevent the stored power from reversely flowing in the event that the generation power runs out. However, the major cause of lowering the charge efficiency lies in loss due to a forward voltage drop across the diode element 601. Accordingly, the use of a diode element with a low forward voltage drop improves the charge efficiency. Meanwhile, the major cause of preventing effective utilization of the power stored on the power storing means 40 is current loss due to reverse current through the diode element 601. That is, it is satisfactory to use such a diode element that is low in forward voltage drop but less in reverse current. However, for the diode element, decrease in forward voltage drop and reduction in reverse current are in relationship of trade off. That is, there has been a problem that it is impossible to realize an electronic portable appliance smaller in size and lighter in weight and operable over a longer time so long as a diode element is used in the above-stated portion.
It is therefore an object of the present invention to provide an electronic portable appliance which is improved in charge efficiency but reduced in useless power such as reverse current, in order to realize reduction of size and weight and longer time operation of the apparatus.
An electronic portable appliance of the present invention to be driven on generation power is configured by a power feed means formed by only a power generating means or a combination of a power generating means and a booster means, a power storing means for storing power of the power feed means, a drive circuit to be operated on power of the power feed means or power stored on the power storing means, a switch means provided on a charging path for charging power of the power feed means to the power storing means to have a function of flowing a charge current and cutting off a reverse current and a feature of having a resistor component to produce a potential difference in the event a current flow, a voltage comparator circuit for comparing voltages on between a charging path point forward of the switch means and a charging path point backward of the switch means, and a control circuit for controlling the switch means depending on a result of comparison by the voltage comparator circuit.
As discussed before, the resistance component possessed by the switch means produces a potential difference at respective ends of the switch means during charging or current reverse flow. It therefore possible for the voltage comparator circuit in the control circuit to perform stable voltage comparison. Thus, realized is a control circuit capable of stably controlling the switch means.
Accordingly, the switch means and control circuit can realize an equivalent function to the diode element used in the conventional electronic portable appliance. In the case of large charge current, the switch means decreases the efficiency of charging to a degree corresponding to the resistance component due to voltage drop through the resistance component. Where the charge current is low, there is almost no decrease of charge current due to voltage drop through the resistance component. Moreover, reverse current is suppressed extremely low. Accordingly, where only a certain degree of charge current occurs, it is possible to improve the charge efficiency and decrease the reverse current.
Furthermore, the invention in the above configuration is structured that the resistance component of the switch means is reduced in resistance value as low as possible. Instead, a resistor element is provided in series with the switch means so that a potential difference is produced during charging or reverse current flow by the resistor element.
Due to this, it is possible to set to produce an optimal potential difference upon charging or reverse current flow, by changing the resistance element in accordance with the ability of the power feed means. Accordingly, labor and time can be omitted in designing an especial switch means having a resistance component with a resistance value meeting the ability of the power feed means or searching for a switchmeans having a close resistance component to the resistance value.
Furthermore, the invention in the above configuration is structured that a diode element is provided in series with the switch means in place of using the resistor element wherein the diode has a lower forward voltage drop than that of the diode used in the conventional electronic portable appliance.
Due to this, the diode element, in place of the resistor element, can produce a potential difference during charging or reverse current flow. Thus, realized is a control circuit to stably control the switch means, as discussed above. Moreover, the usability of a lower forward voltage drop of a diode element than that of the diode element used in the conventional electronic portable appliance improves the charging efficiency. Moreover, the switch element can cut off reverse current, hence reducing the reverse current. Furthermore, for large charge current the diode element is lower in voltage drop in a charging direction as compared to the resistor element. In such a case, the charging efficiency increases as compared to the structure using the resistor element.
Furthermore, in the above structure, a resistance element is connected in parallel wit h the diode element.
This makes possible charging through the resistor element for low charge current and through the diode element for high charge current, thus enhancing the charging efficiency regardless of the amount of charge current.
Furthermore, the switch means uses a MOS transistor. The MOS transistor is less in turning on/off power and correspondingly reduced in useless power consumption. Furthermore, the switch means can be minimized, resulting in reduction in size and weight for the e electronic portable appliance.
Furthermore, the control circuit is provided with a function to intermittently operate the incorporated voltage comparator circuit and a memory circuit to memorize a last-time voltage comparison result of the voltage comparator circuit until a next operation of the voltage comparator circuit so that the switch means is controlled by the voltage comparison result memorized in the memory circuit. This allows the control circuit to operate with reduced power consumption, correspondingly reducing useless power.
Furthermore, the drive circuit has an oscillation circuit or frequency dividing circuit so that an intermittent pulse is created based on an output of the oscillation circuit or frequency dividing circuit which is required to intermittently operate the voltage comparator circuit of the control circuit. This eliminates the necessity for the control circuit to have an oscillation circuit or frequency dividing circuit to create an intermittent pulse, correspondingly reducing power consumption in the control circuit and hence reducing useless power as stated above.
Furthermore, the power feed means has a power generating means, an oscillation circuit and a booster circuit to increase the electromotive force voltage of the power generating means by utilizing an output signal of the oscillation circuit so that an intermittent pulse is created based on an output signal of the oscillation circuit to intermittently operate the voltage comparator circuit of the control circuit. Due to this, the control circuit does not require an oscillation circuit conventionally required to create an intermittent pulse, correspondingly reducing current consumption of the control circuit and hence useless power.